DENTITION
The diet of an animal, generally determines its dentition.
For example, the dentition of a carnivore is different from that of a herbivore or omnivore.
The teeth play a major role in the digestion of food. They help to divide food into smaller pieces.
TYPES OF TEETH AND THEIR RELATION TO FOOD
The characteristics of teeth make up
dentition. In mammals, for example, the teeth vary in size, shape and function – this is known as heterodont dentition.
Vertebrates such as fish, amphibians and reptiles have teeth of the same size, shape and function – this is described as homodont dentition.
Dentition of carnivores
Carnivores are fresh eating animals, e.g. lion, dog, cat. They have highly
specialized teeth.
The characteristics of dentition in
carnivore are:
1. Small, chisel-shaped incisors for seizing prey.
2. Long, conical, pointed and slightly inward-curved canines, used to hold and kill the prey and tear the fresh.
3. Small premolars and molars, except for the first lower molar and third upper molar which are very large. They are called carnassial teeth.
4. Smooth sides and sharp cups and edges that run along the jaw line, used for scraping fresh off bones.
5. Molars have blunt cusps for crushing bones.
Dentition of herbivore
Herbivores are animals that eat only plants,
e.g. goat, cattle, rabbit.
Characteristics of carnivore dentition
1. Long, chisel shaped incisors for cutting and gnawing vegetation.2. File-like premolars and molars with flat-ridged surfaces for grinding plant materials.
3. Absence of canine but instead, a large gap called a diastema between the incisors and premolars.
4. No canines in the upper jaw with poorly developed canines in the lower jaw.
Dentition of omnivores
Omnivores are animals that feed on both animals and plants. Their teeth are not highly specialised.
THE DENTAL FORMULA
Dental formula is the summary of the number, type and arrangement of teeth in the half of the lower and upper jaw of an animal.
The 32 teeth in an adult humans, for example, can be summarized as
i 2/2, c 1/1, pm 2/2, m 3/3,
where the initials are incisors (i), canines (c), premolars (pm),
and molars (m) respectively.
The total number of teeth in an adult human can therefore be obtained by multiplying the sum of the figures indicated in the dental formula by
2, i.e. 2 (4+2+4+6) = 32.
STRUCTURE OF THE TOOTH
Teeth develop from a group of cells in the skin overlying the jawbones.
Humans andother animals have different kinds of teeth.
Although teeth differ is size and shape and perform different function, their internal structure is similar.
Parts of the tooth
Crown: This is the part that projects above the gum
Root: The part which is buried in a socket in the jawbone. Some teeth have a single root while others have two or three roots.
Enamel: This is a layer of thin, hard, shiny material composed mainly of calcium phosphate.
It covers the crown.
Dentine: The dentine is located beneath the enamel and extended into the root. It makes up the greatest bulk of the tooth.
Dentine is a very hard bone, but is not as hard as the enamel.
Fine channels, containing living materials, pass through the dentine. The dentine encloses a central pulp cavity.
The pulp cavity: The pulp is made up of blood vessels, tooth-forming cells and nerve fibres with sensory nerve endings, which penetrates the dentine, making it sensitive to pain and temperature changes.
Cement: Teeth are fixed in the lower bone by the cement, which is a hard bony substance that covers the outside of the root.
Periodontal fibres: Attached to the cement are tough periodontal fibres which run into the jaw bone. These fibres hold the tooth in its socket and permit slight tooth movements that cushion the tooth from excessive jarring when it hits a hard object.
Types of teeth and their functions in
mammals
Teeth in mammals come in four different types – incisors, canines, premolars and molars.
Incisors
These are the two pairs of teeth found in
the front part of each jaw.
Features of incisors
1. They are chisel shaped.
2. They have broad, flat cutting edge for biting and cutting food.
3. They have a single root.
Canines
There are two canines next to the incisors.
Features of canines
1. They are bluntly pointed.
2. They are used for cutting and biting solid foods.
Premolars
These are found in either half of the jaws.
Features of premolars
1. They have flat tops.
2. They have cusps (pointed ridges).
3. They have one or two roots.
Molars
They make the three final teeth on each half of each jaw.
Features of molars
1. They have flat tops.
2. They have four or five cusps.
3. They have three roots (upper molars) and two roots (lower molars).
The premolars and molars are collectively known as cheek teeth.
Set of teeth in humans
Mammals have two sets of teeth in their lifetime.
The first set of 20 teeth is called milk teeth and is found in young humans.
They are made up of incisors, canines and premolars. These teeth fall out one by one in early life and are replaced by the permanent teeth.
The last molar teeth in each jaw is called wisdom teeth because they are the last to appear when the person is between 17 and 25 years old.
Care of the teeth in humans
In order to prevent and control dental problems, it is important for us to take good care of the teeth. Lack of proper care of the teeth results in dental caries (tooth decay) and periodontal disease.
Dental caries (tooth decay)
This is a dental condition caused when bacteria feed on sugar and starch in the mouth. Their enzymes react with the sugar and starch and produce acid.
The acid reacts with calcium in the enamel and dentine and breaks down the enamel and dentine creating a hole in the tooth.
Bacteria move on to feed on the pulp and the sensitive nerve ending which causes toothache. At the early stages, the tooth can be repaired.
Causes of dental caries
1. Lack of hard food
2. Lack of vitamin D
3. Eating too much sugar
4. Lack of calcium
5. Improper cleaning of teeth
Periodontal disease:
This is caused by the accumulation of food debris, saliva and bacteria to form a hard thin coating on the surface of the teeth called plaque. The plaque spreads down to the gum causing the gum to swell, breed, recede and give off bad breath. The recession of the gum causes the teeth to fall out.
Causes of periodontal disease
1. Lack of vitamin A and C
2. Improper cleaning of teeth
3. Lack of massage of the gum
Ways of preventing dental problems
The following are necessary measures to prevent the above diseases:
1. Cleaning the teeth regularly
2. Regular visit to the dentist
3. Eating food rich in minerals and vitamins
4. Using the teeth properly; for example, not using the teeth to open bottles or screws.
Digestive system is a network of organs and enzymes which converts the complex food (i.e. carbohydrates, proteins, lipids etc) eaten into small and absorbable forms for the use of the body.
Or
Digestion is the breakdown of complex food substances into simple, soluble and absorbable forms.
Structure and functions of the
digestive system of mammals
The digestive system of mammals is made up of the gut or alimentary canal and other organs and glands.
The alimentary canal is
a muscular tube made up of the following parts:
Mouth
Digestion starts from the mouth, where food is chewed with the teeth. Chewing (or mastication) breaks down solid food into smaller particles.
Salivary glands produce
saliva which:
contains the an enzyme called saliva amylase that converts starch into maltose.
is slightly alkaline and keeps the pH of the mouth approximately neutral which help in the action of saliva amylase.
mixes with the food during chewing, making it soft and easier to swallow.
Oesophagus
A muscular tube that connects the mouth to the stomach. Food passes down the oesophagus through contraction and relaxation of the circular muscles of the gut. This action is called peristalsis.
The stomach
The stomach is a sac-like organ that
produces gastric juice which contains:
hydrochloric acid (sterilizes food, ends action of saliva amylase, provide acidic pH for action of the enzyme
pepsin which converts proteins to
polypeptides,
mucus which forms a protective inner lining to the animal wall and
rennin which solidifies liquid proteins so that they will remain in the stomach for pepsin to work on.
The contractions of the stomach wall
muscles churn the food into chyme (a creamy-white mixture of food substance).
At this stage glucose and alcohol are
absorbed from the food into the blood stream.
Duodenum
The chyme from the stomach passes the pyrolic sphincter into the duodenum where the hormone secretin is released into the bloodstream.
Secretin then stimulates the gall bladder to release bile and the pancreas to release pancreatic juice into the duodenum.
Liver
The liver is one important organ which is responsible for most chemical activities in the body.
Functions of the lever
1. Production of bile which emulsifies or breaks down fats, converts glucose to glycogen, produces urea (the main substance of urine), makes certain amino acids (the building blocks of proteins).
2. Filtration of harmful substances from the blood (such as alcohol).
3. Storage of vitamins and minerals
(vitamins A, D, K and B12)
4. Maintaining the proper level or glucose in the blood.
5. Production of cholesterol; it produces about 80% of the cholesterol in the body
6. Production of heat to the body through chemical activities.
7. Production of some proteins such as fibrinogen in the blood plasma.
8. Destruction and stopping of hormones from unlimited action.
9. Conversion of excess fats into glycerol and fatty acids.
10. Excretion of excess cholesterol and old red blood cells from the body.
Bile
Bile is alkaline and raises the pH of the chyme. It emulsifies fat by changing large fat globules into small fat droplets.
Emulsification increases the surface area of the fat making the digestion of fat by enzymes more efficient.
Pancreas
The pancreas secrets pancreatic juice which is alkaline and therefore raises the pH of the chyme.
The pancreatic juice contains
amylase which converts starch to
maltose,
trypsin which converts protein to
peptides and polypeptides and
lipase which converts fat to fatty acids and glycerol.
All these enzymes digest food as is passes though the duodenum into the ileum. Ileum (small intestines)
The digestion process ends in the ileum.
The walls of ileum secrets:
lipase which converts all remaining fats into fatty acids and glycerol;
maltase which converts maltose to
glucose;
lactase which converts lactose to
glucose and galactose,
sucrase which converts sucrose to
glucose and fructose,
erepsin which converts peptides to
amino acids and
enterokinase
which converts
trypsinogen to trypsin.
The small molecules of glucose, amino
acids, fatty acids, and glycerol are the end
products of digestion in mammals and are
absorbed into the bloodstream by a process
known as diffusion.
The ileum contains thousands of
microscopic projections called
villi
(singular, villus), which increases the
surface area of the ileum and facilitates the
absorption process. Undigested food passes
into the colon.
Colon (large intestines)
The colon is responsible for the absorption
of water from the undigested food. It
contains some bacteria which digest the
cellulose and produce vitamin B and K
which are absorbed into the body. The
remains of the undigested food pass on to
become faeces.
Organ/ gland
Secreted enzyme
Enzyme action
Mouth (salivary glands)
Salivary amylase
Starch to maltose
Oesophagus
Passage of food to
stomach
Stomach
Pepsin
Rennin
Hydrochloric acid
Polypeptides
Solidifies protein
sterilizes food; provide acidic pH
for action of the enzyme
Duodenum
Secretin
Stimulates gall bladder to release
bile and pancreas to release
pancreatic juice
Liver
Bile
Emulsifies starch
Pancreas (pancreatic juice)
Amylase
Trypsin
Lipase
Starch to maltose
Protein to peptides and
polypeptides
Fatty acids to glycerol
Ileum
Lipase
Maltase
Lactase
Sucrose
Erepsin
Fats into fatty acids and glycerol
Maltose to glucose
Lactose to glucose
Sucrose to glucose
Peptides to amino acids
Enterokinase
Trypsinogen to trypsin
Colon
Absorption of water from
undigested food
Rectum
Temporary storage for faeces
Rectum
The faeces move into the rectum, where
they are stored and released periodically
through the anus. The removal of food
from the rectum is known as egestion. Not
to be confused with ingestion, which is the
act of putting food into the mouth?
The term digestion refers to the breakdown of complex food into smaller form which can be absorbed by the body. Digestion occurs as a result of chemical or mechanical processes in the body. Digestion is very important because it allows the body to gain energy through ingested food.
Different food substances have different modes of digestion.
Digestion of carbohydrates
Carbohydrate digestion starts in the mouth.
Saliva contains ptyalin (salivary amylase) which converts starch to maltose.
In the stomach, HCl in gastric juice sterilizes the food.
The food is churned into liquid paste called chyme.
In the duodenum, the bile secreted by the liver neutralizes the chime.
Pancreatic amylase secreted by the pancreas converts starch into maltose sugar.
In the ileum, the enzyme maltase converts maltose into glucose, which is the end-product of starch digestion.
Digestion of proteins
Protein digestion starts in the stomach.
Pepsin converts proteins to peptones.
HCl sterilizes it; it is churned to chime and sent to duodenum where the bile neutralizes it.
In the duodenum, the typsin which is secreted by the pancreas converts peptones into amino acids.
Digestion of fats
The digestion of fat starts in the duodenum.
Gall bladder releases bile into the duodenum.
Bile neutralizes and emulsifies the fat.
The enzyme lipase secreted by the pancreas and the wall of the small intestines converts emulsified fat into fatty acids and glycerol, which is the end-product of fat digestion.
End-products of digestion Food
End Product
Carbohydrates Glucose
Proteins Amino acids
Fats Fatty acids and glycerol
Uses of Digested Food
The end-product of digestion is assimilated (taken up) by the cells in various parts of the body.
Glucose and others move into the blood by diffusion and enter the liver through the hepatic portal vein. In the liver excess glucose is converted to glycogen and stored.
Some of the monosaccharides enter body cells where they are respired.
Amino acids are also assimilated into the liver though the hepatic portal vein.
Some enter the body cells where they are used to form protein for growth, repair of damaged and worn-out tissues and formation of enzymes and hormones.
Excess amino acids are excreted out of the body as urea.
Fatty acids and glycerol come together again to form fats, which enters the lymph system before entering the bloodstream. They are stored as fat or respired to release energy.
Assimilation is the process whereby digested food substances are absorbed into the bloodstream.
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